PROJECT SUMMARY/ABSTRACT Obstructive sleep apnea syndrome (OSAS) is common in children and adults with Down Syndrome (DS), but its impact upon quality of life, behavior, cognitive function, diabetes, and heart health are not known. Significant residual OSAS is common after adenotonsillectomy and further highlights the need to better delineate the contribution of OSAS to common morbidities and compromised quality of life in DS. A major challenge to both clinical care and research related to OSAS is the testing required for diagnosis. In youth, testing for OSAS requires an overnight stay in a sleep laboratory. Accessing centers with expertise in pediatric OSAS and the care of children with intellectual disabilities is limited. Additionally, the testing is expensive, and children may reject the testing due to behavior and sensory issues. The frequency of screening has yet to be defined, an issue complicated by the relative inability of standard interviews and questionnaires to discern OSAS risk. Our long-term objective is to study the relationship of OSAS and its treatment upon quality of life, behavior, cognitive function, and heart health. To this end, this study proposes 1) to test the acceptability and feasibility of home sleep apnea testing in adolescents with Down Syndrome. 2) to test for patient factors that contribute to the acceptability and feasibility of home sleep apnea testing in adolescents with Down Syndrome. 3) to determine how well home apnea sleep testing diagnoses OSAS in adolescents with Down Syndrome. To accomplish these aims, youth age 10-20 years with DS will undergo home sleep apnea testing and standard overnight sleep testing in a laboratory. Caregivers will be taught how to set-up the system and study staff will be available to address problems. Caregivers and participants will complete questionnaires related to how easily the sleep testing was performed at home, if they encountered any issues with set-up or with the various components staying in place overnight, and quality of life. The home sleep apnea test results will be compared with results from the standard in-lab sleep test. These preliminary studies will help determine if home sleep apnea testing is feasible, if a subset of youth do better or worse with home sleep apnea testing, and how well it performs as a diagnostic test. If using this test is feasible, acceptable, well-tolerated, and performs well as a diagnostic test, a clinical trial will be pursued that tests the impact of OSAS treatment upon quality of life, behavior, cognitive function, and heart health in adolescents with Down Syndrome.